Stability improvement of aluminum hydroxide in PVC compound

ABSTRACT

An aluminum hydroxide composition is disclosed, having diminished tendency to cause discoloration on heating at 177° C. of a plastic composition whose major polymeric component is polyvinyl chloride, comprising aluminum hydroxide and an amount, effective in diminishing discoloration, of at least one inorganic perchlorate salt selected from the group consisting of alkali metal perchlorates and alkaline earth metal perchlorates.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to aluminum hydroxide having a diminishedtendency to cause discoloration when compounded with a plasticcomposition at an elevated temperature, typically 180° C. In particular,the invention relates to aluminum hydroxide in a plastic composition inwhich the major polymeric component is a vinyl chloride polymer such aspolyvinyl chloride, conveniently abbreviated pvc.

[0003] 2. Description of the Related Art

[0004] For a review of the utilization of aluminum hydroxide as anadditive and compounding ingredient in plastic compositions,particularly relating to the use of aluminum hydroxide as a flameretardant, reference can be made to Chapter 81 by Frank Malesky in“Handbook of Plastics Additives and Modifiers”, J. Edenbaum, ed., (NewYork: Van Nostrand Reinhold 1992), pages 1071-1085.

[0005] The problem of imparting to pvc a sufficient heat processingstability at temperatures at which the polymer becomes sufficientlyfluid or softened to permit shaping is of long standing. It has beenresolved in principle by the addition to the polymer of variouscombinations of known heat stabilizers. Given the great versatility ofplastic compositions in which pvc is the major polymeric component,however, the selection of the right stabilizer or stabilizer combinationfor any given composition remains an empirical art in which theories andpredictions are of limited usefulness.

[0006] There exists a prodigiously large literature relating tostabilizers for pvc. For a convenient review and classificationreference can be made to Chapters 16-20 in the above-cited “Handbook”,pages 208-337.

[0007] The following individual disclosures are believed to representthe closest prior art to the present invention.

[0008] M. Tadenuma et al., U.S. Pat. No. 5,004,776 disclosed a thermallystabilized chlorine-containing resin composition comprising a stabilizerconsisting essentially of (a) an overbased alkaline earth metalcarboxylate or phenolate complex, (b) zeolite, (c) calcium hydroxide and(d) a complex of at least one metal perchlorate selected from the groupconsisting of sodium, magnesium, calcium and barium perchlorates with atleast one compound selected from the group consisting of polyhydricalcohols and their derivatives. The chlorine-containing resincomposition may further comprise a known stabilizer forchlorine-containing resins, a known co-stabilizer and other knownadditives, for example (among others) an inorganic metal salt compound.The inorganic compound includes, for example, magnesium oxide, calciumoxide, calcium phosphate, aluminum hydroxide, synthetic hydrotalcite andthe like.

[0009] Y. Sato al., U.S. Pat. No. 5,025,051 disclosed a synthetic resincomposition comprising (A) 100 parts by weight of a synthetic resin, and(B) 0.01 to 10 parts by weight of a mixed product of (a) a compoundhaving at least one piperidyl group, (b) perchloric acid, and (c)optionally an inorganic substance other than perchloric acid. As theinorganic substance other than perchloric acid, there are d disclosed,for example, an oxide, hydroxide, inorganic acid salt, basic inorganicacid salt or double salt of at least one metal selected from the groupconsisting of Li, Na, K, Mg, C, Sr, Ba, Zn, Al, Sn and Pb, further ametallic aluminum powder, or a metal oxide such as SnO2, TiO2, or ZrO2.As the oxide of the metal there are mentioned, for example, MgO, CaO,BaO, ZnO, SrO2, or PbO, and as the hydroxide of said metal there arementioned, for example, LiOH, Mg (OH)2, Ca (OH)2 or Al(OH)3.

[0010] K. Bai et al., U.S. Pat. No. 5,034,443 disclosed that a blend ofsodium perchlorate hydrate and calcium silicate provides improved longterm heat stability to a polyvinyl chloride resin containing aconventional heat stabilizer, and that a combination of a solution ofsodium perchlorate in water with calcium silicate and a non-absorbingdiluent powder such as calcium carbonate provides a free-flowing powdercomposition of reduced hazard level. Other non-absorbing diluent powdersinclude zeolites, silica, alumina, PVC resins, barium sulfate and thelike.

[0011] Watanabe et al., U.S. Pat. No. 5,190,700 disclosed a flameretardant for a powder halogen-containing vinyl resin which comprises(A) 5 to 40 parts by weight of at least one alkali metal compound oflithium, sodium and potassium calculated as the formula M2O where M issaid alkali metal (B) 0.2 to 10 parts by weight of a perchloric acidradical in the form of the acid or a salt or amine thereof, calculatedas perchloric acid radical (ClO4), and (C) 1-50 parts by weight of ahydrophobic dispersing agent having a boiling point or a decompositiontemperature of 200° C. or higher, based on 100 parts by weight ofantimony pentoxide (Sb2O5). Watanabe also acknowledges that a variety offlame retardants have been used, including inorganic materials such asantimony trioxide (Sb2O3), sodium antimonite, aluminum hydroxide,zirconium oxide, zinc borate and borax.

[0012] R. Drewes et al., U.S. Pat. Nos. 5,519,077 and 5,543,449disclosed compositions comprising (a) pvc, (b) perchloric acid or aperchlorate, (c) a terminal epoxide compound and (d) an antioxidant('077) and (a) flexible pvc, (b) perchloric acid or a perchlorate, (c) aterminal epoxide compound ('443). In each case it is also disclosed thatthe compositions can contain further additives. These are, for example,fillers and reinforcing materials (for example calcium carbonate,silicates, glass fibers, talc, kaolin, chalk, mica, metal oxides andhydroxides, carbon black or graphite). The fillers used are, forexample, chalk, kaolin, china clay, talc, silicates, glass fibers, glassbeads, sawdust, mica, metal oxides or hydroxides, carbon black,graphite, rock flour and barytes.

[0013] None of the above disclosures mention a tendency to discolorcaused by aluminum hydroxide.

[0014] Thus, while the well established and successful conventional heatstabilizers provide effective stabilization to the substrate polymercomposition whose major polymeric component is pvc at elevated heatprocessing temperatures during standard processing, they may not provideeffective stabilization to additives contained within the polymer duringsuch heat processing. For example, the use of aluminum hydroxide in suchcompositions is not without limitations. It has been found that oneimportant limitation is the tendency of an otherwise adequatelystabilized pvc composition to discolor in the presence of aluminumhydroxide, with the intensity of discoloration increasing withincreasing use levels of aluminum hydroxide in such composition.

[0015] It is therefore a general object of the present invention toprovide a plastic composition containing aluminum hydroxide having adiminished tendency to discolor at processing temperatures of the orderof 180° C.

[0016] It is also an object of the invention to provide an aluminumhydroxide composition having a diminished tendency to discolor whenincorporated in a plastic composition whose major polymeric component ispvc.

[0017] It is also an object of the invention to provide an aluminumhydroxide composition having enhanced flame retardant properties whenincorporated in a plastic composition whose major polymeric component ispvc.

[0018] It is a further object of the invention to provide a method ofstabilizing a plastic composition whose major polymeric component is pvcand which contains aluminum hydroxide.

SUMMARY OF THE INVENTION

[0019] In accordance with this invention, there is provided an aluminumhydroxide composition having diminished tendency to cause discolorationon heating at 177° C. of a plastic composition whose major polymericcomponent is polyvinyl chloride, comprising aluminum hydroxide and anamount, effective in diminishing discoloration, of at least oneinorganic perchlorate salt selected from the group consisting of alkalimetal perchlorates and alkaline earth metal perchlorates. The effectiveamount of the perchlorate salt ranges from 0.03 parts by weight to 3parts by weight per 100 parts by weight of aluminum hydroxide.

[0020] Also in accordance with this invention, there is provided aplastic composition having diminished tendency to discolor on heating at177° C. in the presence of aluminum hydroxide, comprising polyvinylchloride, aluminum hydroxide, and an amount, effective in diminishingthe tendency to discolor, of at least one inorganic perchlorate saltselected from the group consisting of alkali metal perchlorates andalkaline earth metal perchlorates. The amount of aluminum hydroxide issuitably a flame-retardant amount in the range from 15 parts by weightto 150 parts by weight per 100 parts by weight of polyvinyl chloride.The amount of the perchlorate salt s in the range from 0.03 parts byweight to 3 parts by weight per 100 parts by weight of aluminumhydroxide.

[0021] Moreover, in accordance with this invention, there is provided amasterbatch composition adapted for safe storage, transport, andsimplified compounding with a plastic composition whose major polymericcomponent is polyvinyl chloride, comprising aluminum hydroxide and atleast one inorganic perchlorate salt selected from the group consistingof alkali metal perchlorates and alkaline earth metal perchlorates. Themasterbatch according to the invention can contain from 7 parts byweight to 500 parts by weight of the perchlorate salt, calculated on adry basis, per 100 parts by weight of aluminum hydroxide. Themasterbatch according to the invention can additionally include water,calcium silicate, and inert inorganic diluent powder as required.

[0022] A masterbatch according to the invention simplifies thecompounding of an aluminum hydroxide containing plastic compositionwhose major polymeric component is polyvinyl chloride with the effectiveamount of perchlorate salt required according to the invention bysubstituting for it a more proportionate quantity of a more easilyhandled and transported masterbatch as defined, along with additionalaluminum hydroxide and other compounding ingredients as required.

[0023] Also provided in accordance with this invention is an insulatedelectrical conductor comprising a metallic conductor, a first insulatinglayer comprising flexible polyvinyl chloride surrounding the conductor,and a second layer surrounding the first insulating layer as a plenum orjacket. The second layer comprises polyvinyl chloride, a sufficientquantity of plasticizer to impart flexibility to the composition,aluminum hydroxide, and an amount, effective in diminishing the tendencyto discolor, of at least one inorganic perchlorate salt selected fromthe group consisting of alkali metal perchlorates and alkaline earthmetal perchlorates. The amount of aluminum hydroxide is suitably aflame-retardant amount in the range from 15 parts by weight to 150 partsby weight per 100 parts by weight of polyvinyl chloride. The amount ofthe perchlorate salt s in the range from 0.03 parts by weight to 3 partsby weight per 100 parts by weight of aluminum hydroxide.

[0024] Surprisingly, it has been found that the flame retardance of pvccompositions according to the invention comprising a flame retardantamount of aluminum hydroxide is enhanced in comparison to similarcompositions not including an effective amount of such inorganicperchlorate salt. The flame-retardant amount is in the range from 15 to150 parts by weight of aluminum hydroxide per 100 parts by weight ofpvc.

DETAILED DESCRIPTION OF THE INVENTION

[0025] Throughout this specification and the accompanying claims, theterm polyvinyl chloride and its abbreviation pvc are used to refer tovinyl chloride polymers in general, including vinyl chloridehomopolymer; copolymers of vinyl chloride as the major monomer withminor amounts of one or more unsaturated monomers such as vinyl acetate,vinylidene chloride, vinyl alkyl ethers, ethylene, propylene, dialkylmaleates and acrylonitrile; and blends of a vinyl chloride polymer withequal or lesser amounts of polymeric modifiers such as acrylic andmethacrylic ester polymers, butadiene polymers, styrene polymers,acrylonitrile polymers, and copolymers of two or more of the hereindicated monomers, chlorinated polyethylene and chlorinated vinylchloride polymers. Additional representatives of the class of polymermaterials to which the term polyvinyl chloride is here applied aredisclosed by Wehner et al., U.S. Pat. No. 6,194,494 B1, at column 44line 29 to column 45 line 16, which disclosure is here incorporated byreference.

[0026] The alkali metal and alkaline earth metal perchlorates usedaccording to this invention include barium perchlorate, calciumperchlorate, lithium perchlorate, magnesium perchlorate, potassiumperchlorate, sodium perchlorate, and strontium perchlorate. Anhydroussolid forms, hydrated solid forms, and aqueous solutions of theseperchlorate salts can be used according to the invention. Sodiumperchlorate is preferred. Sodium perchlorate monohydrate is particularlypreferred.

[0027] PVC used according to this invention can be rigid or flexible.Flexible PVC is preferred. Flexibility is imparted to PVC as known inthe art by such techniques as limiting thickness of unmodified vinylchloride homopolymer to 0.05 mm or less, by copolymerization of vinylchloride with 10-20% of such comonomers as vinyl acetate (so-calledinternal plasticization), and particularly by compounding withcompatible liquids known as plasticizers. Many suitable plasticizers areknown in the art, including in particular the esters of dicarboxylic andtricarboxylic acids such as adipic, citric, phthalic and trimelliticacids with alcohols having 6-12 carbon atoms, preferably dialkylphthalates and trialkyl trimellitates having 7 to 11 carbon atoms in thealkyl groups. Additional representatives of the class of suitableplasticizers are disclosed by Wehner et al., U.S. Pat. No. 6,194,494 B1at column 37 line 36 to column 38 line 51, which disclosure is hereincorporated by reference. Use levels of plasticizers when present canrange from 5 parts by weight to 125 parts by weight per 100 parts ofpvc.

[0028] PVC compositions according to this invention usually contain atleast one heat stabilizer. In principle, any known heat stabilizer canbe used. Preference is usually given to environmentally acceptablestabilizers from which such toxic heavy metals as arsenic, cadmium,lead, and thallium are substantially excluded. Particularly preferredmetal containing heat stabilizers are barium, calcium, magnesium,strontium, and zinc salts of aliphatic and aromatic non-nitrogenousmonocarboxylic acids having 6 to 24 carbon atoms. Particularly preferrednon-metallic heat stabilizers are aliphatic and aromatic phosphites,substituted phenols having a molecular weight of at least 200 daltons,ethers and esters having epoxide groups and molecular weight of at least200 daltons and 1,3-dicarbonyl compounds having molecular weight of atleast 200 daltons. Additional categories of suitable heat stabilizersare disclosed by Wehner et al., U.S. Pat. No. 6,194,494 B1, at column 1line 4 to column 2 line 5, and many individual representatives of thesecategories are disclosed at column 2 line 46 to column 37 line 25 andcolumn 39 line 8 to column 42 line 27. These disclosures are hereincorporated by reference. Use levels of heat stabilizers when presentcan range from 0.01 to 10 parts by weight per 100 parts of pvc. Largeramounts can be used but are seldom required.

[0029] Conventional lubricants, flame retardants, colorants, fillers andother compounding ingredients and additives can be included in thecomposition of the invention as required. For a compilation of suchmaterials, reference can be had to Wehner et al., U.S. Pat. No.6,194,494 B1, at column 37 lines 26-35, column 38 line 52 to column 39line 7, which disclosure is here incorporated by reference.

[0030] The following examples are offered by way of illustration and notof limitation of the invention as defined by the appended claims.

EXAMPLES 1-5

[0031] The effectiveness of compositions of the invention was observedin a typical plenum wire compound formulation, that is a formulation ofa flexible flame retardant outer sheath or plenum for a wire or othermetallic conductor surrounded by a layer of primary insulation andfurther surrounded by the outer sheath or plenum. All quantities aregiven in parts by weight.

[0032] Thus, the typical plenum wire compound base formulation containedPVC resin 100.0 Phthalate ester plasticizer 50.0 Omya F brand of calciumcarbonate 12.0 Antimony trioxide second flame retardant 5.0 Stearic acid0.25 Ba/Zn solid stabilizer 8.0 ATH aluminum hydroxide 50.0

[0033] Various amounts of 60% Na perchlorate monohydrate aqueoussolution (abbreviated NaP-60) were blended with this base formulationusing a two roll mill, as shown below for each Example, and samples cutfrom each milled sheet were tested for static oven stability at twotemperatures, 350° F. (177° C.) sampled at 15 minute intervals and 375°F. (190° C.) sampled at 10 minute intervals. EXAMPLE Control A 1 2 3 4 5NaP-60 parts actual none 0.5 1.0 1.5 2.0 3.0 NaP-60 parts/100 ATH none1.0 2.0 3.0 4.0 6.0 As dry NaClO₄ per 100 none 0.48 0.96 1.44 1.92 2.88ATH

[0034] The Control A PVC compound without perchlorate initiallydiscolored to brown in 90 minutes at 177° C. and 40 minutes at 190° C.and turned to dark brown in 105 minutes at 177° C. and in 50 minutes at190° C., but with perchlorate treated ATH, the test compound colorchange was much less.

[0035] At 177° C. oven test, the color change of Examples 1-5 is minimal(no sign of brown color in 120 minutes) and at 190° C. the Examples 1-5compounds containing the perchlorate and ATH shows improved long termstability compared to Control A. Also the perchlorate containing ATH hadimproved flame and smoke properties of plenum compounds over that usingATH without perchlorate.

EXAMPLES 6-12

[0036] The effectiveness of the composition of the invention wasobserved in a similar plenum base formulation with varied levels ofsodium perchlorate monohydrate supplied in two different physical forms.PVC resin 100.0 Dialkyl phthalate plasticizer 47.0 Omya F brand ofcalcium carbonate 12.0 Antimony trioxide second flame retardant 8.0Stearic acid 0.3 Ba/Zn solid stabilizer 6.0 ATH aluminum hydroxide 60Powder blend containing NaClO₄ (note) variable NaP-60 aqueous solutionvariable

[0037] The amounts of ATH aluminum hydroxide and NaP-60 sodiumperchlorate monohydrate solution blended with each Example formulationand tested for static oven heat stability at 350° F. (177° C.) and 400°F. (205° C.) are shown below: EXAMPLE Control B 6 7 8 9 Powder blendactual none 0.25 0.5 1.0 2.0 As NaP-60 parts solution none 0.083 0.1670.33 0.67 As NaP-60 parts/100 ATH none 0.167 0.33 0.67 1.33 As dryNaClO₄ per 100 ATH none 0.08 0.16 0.32 0.64 EXAMPLE 10 11 12 NaP-60parts solution actual 0.15 0.3 0.6 As NaP-60 parts/100 ATH 0.3 0.6 1.2As dry NaClO₄ per 100 ATH 0.144 0.288 0.51

[0038] The Control B PVC compound without perchlorate initiallydiscolored to brown in 90 minutes at 177° C. and 20 minutes at 205° C.and turned to dark brown in 105 minutes at 177° C. and in 25 minutes at205° C.

[0039] Addition of perchlorate substantially prevented browndiscoloration of Examples 6 to 105 minutes at 177° C. and for the entire120 minute test period at that temperature in Examples 7-12. In the testat 205° C. as little as 0.083 parts of the sodium perchloratemonohydrate solution (contained in 0.25 parts of the powder blend usedin Example 6) was effective in delaying brown discoloration, andincreasing perchlorate levels were increasingly effective.

EXAMPLES 13-15

[0040] The effectiveness of the composition of the invention wasobserved in the plenum base formulation of Examples 6-12 with variedlevels of aluminum hydroxide. PVC resin 100.0 Phthalate plasticizer 47.0Omya F brand of calcium carbonate 12.0 Antimony trioxide second flameretardant 8.0 Stearic acid 0.3 Ba/Zn solid stabilizer 6.0 ATII aluminumhydroxide variable Powder blend containing NaClO₄ (note) variable

[0041] The amounts of ATH aluminum hydroxide, the above powder blendcontaining NaP-60 sodium perchlorate monohydrate solution and theresulting amount of sodium perchlorate contained in each Exampleformulation and tested for static oven heat stability at 350° F. (177°C.) and 400° F. (205° C.) are shown below: Control Control ControlControl Control EXAMPLE C D E F G ATH aluminum none none 10 20 40hydroxide Powder blend actual 0.5  none none none none As NaP-60 partssolution 0.167 none none none none As NaP-60 parts/100 N/A none nonenone none ATH As dry NaClO₄ per 100 N/A none none none none ATH ControlEXAMPLE H 13 14 15 ATH aluminum hydroxide 60 10 20 60 Powder blendactual none 0.5 0.5 0.5 As NaP-60 parts solution none 0.167 0.167 0.167As NaP-60 parts/100 ATH none 1.67 0.83 0.28 As dry NaClO₄ per 100 ATHnone 0.80 0.40 0.13

[0042] The Control C and Control D compounds represent a comparison thatmeasures the stabilizing effectiveness of sodium perchlorate in theabsence of aluminum hydroxide. Both Control C and Control D also containthe same amount of barium-zinc stabilizer. It can be seen that there isa certain favorable effect of the sodium perchlorate in Control C.Control C showed the first sign of brown discoloration at 105 minutes at177° C. and at 15 minutes at 205° C., while Control D showed the firstsign of brown discoloration at 90 minutes at 177° C. and at 10 minutesat 205° C. Control C also turned to dark brown at 30 minutes at 205° C.while Control D turned to dark brown at 20 minutes at 205° C.

[0043] Controls D, E, F, G and H represent a comparison that measuresthe effect of increasing levels of aluminum hydroxide from zero to 10,20, 40, and 60 parts per 100 parts of pvc.

[0044] The results show that the first sign of brown discoloration aswell as turning dark brown occur progressively earlier as the use levelof aluminum hydroxide is increased. It is seen, therefore, that aluminumhydroxide represents a problem in stabilization over and above thestabilization of pvc.

[0045] Surprisingly, the use of perchlorate in Examples 13-15 presentedan entirely different trend. Thus the addition of 0.5 part of powderblend, representing 0.167 parts of 60% sodium perchlorate monohydratesolution substantially prevented brown discoloration of Examples 13 to15 for the entire 120 minute test period at 177° C. In the test at 205°C. 0.167 parts of the sodium perchlorate monohydrate solution (containedin 0.5 parts of the powder blend) was effective in delaying the firstsign of brown discoloration of the samples containing aluminum hydroxideto 25 minutes, longer than 15 minutes in the absence of aluminumhydroxide (compare Control C and Example 15 both having the sameperchlorate level and the most extreme difference in use level ofaluminum hydroxide, i.e. 0 compared to 60 parts per 100 pvc).

[0046] Thus the stability problem with aluminum hydroxide in pvc iscounteracted and even reversed by the addition of sodium perchlorate inaccordance with the invention.

What is claimed is:
 1. An aluminum hydroxide composition having diminished tendency to cause discoloration on heating at 177° C. of a plastic composition whose major polymeric component is polyvinyl chloride, comprising aluminum hydroxide and an amount, effective in diminishing said discoloration, of at least one inorganic perchlorate salt selected from the group consisting of alkali metal perchlorates and alkaline earth metal perchlorates.
 2. The composition of claim 1, wherein said effective amount is in the range from 0.03 parts by weight to 3 parts by weight per 100 parts by weight of aluminum hydroxide.
 3. The composition of claim 1, wherein said inorganic perchlorate is sodium perchlorate.
 4. The composition of claim 3, wherein said perchlorate is sodium perchlorate monohydrate.
 5. A plastic composition having diminished tendency to discolor on heating at 177° C. in the presence of aluminum hydroxide, comprising polyvinyl chloride, aluminum hydroxide, and an amount, effective in diminishing said tendency to discolor, of at least one inorganic perchlorate salt selected from the group consisting of alkali metal perchlorates and alkaline earth metal perchlorates.
 6. The composition of claim 5, wherein the amount of aluminum hydroxide is a flame retardant amount.
 7. The composition of claim 6, wherein the amount of aluminum hydroxide is in the range from 15 parts by weight to 150 parts by weight per 100 parts by weight of polyvinyl chloride.
 8. The composition of claim 5, wherein the amount of said inorganic perchlorate is in the range from 0.03 parts by weight to 3 parts by weight per 100 parts by weight of aluminum hydroxide.
 9. The composition of claim 5, wherein said inorganic perchlorate is sodium perchlorate.
 10. The composition of claim 5, additionally comprising at least one plasticizer.
 11. The composition of claim 5, additionally comprising at least one heat stabilizer.
 12. The composition of claim 10, wherein said at least one plasticizer is selected from the group consisting of dialkyl phthalates and trialkyl trimellitates having independently in each alkyl group seven to eleven carbon atoms.
 13. The composition of claim 1 1, wherein said at least one heat stabilizer is a barium, calcium, magnesium, strontium, or zinc salt of a non-nitrogenous monocarboxylic acid having 6-24 carbon atoms.
 14. A masterbatch composition adapted for safe storage, transport, and compounding with a plastic composition whose major polymeric component is polyvinyl chloride, comprising aluminum hydroxide and at least one inorganic perchlorate salt selected from the group consisting of alkali metal perchlorates and alkaline earth metal perchlorates, said masterbatch containing from 7 parts by weight to 500 parts by weight of said perchlorate salt per 100 parts by weight of aluminum hydroxide.
 15. The masterbatch composition of claim 14, containing from 30 parts by weight to 150 parts by weight of said inorganic perchlorate salt per 100 parts by weight of aluminum hydroxide.
 16. The masterbatch composition of claim 14, wherein said inorganic perchlorate is sodium perchlorate.
 17. The masterbatch composition of claim 16, wherein said inorganic perchlorate is sodium perchlorate monohydrate.
 18. A method of diminishing the tendency to cause discoloration on heating at 177° C. of an aluminum hydroxide containing plastic composition whose major polymeric component is polyvinyl chloride, comprising the steps of mixing polyvinyl chloride with a masterbatch according to claim 14, and adding thereto additional aluminum hydroxide such that the composition contains from 15 parts by weight to 150 parts by weight of aluminum hydroxide per 100 parts by weight of polyvinyl chloride and from 0.03 parts by weight to 3 parts by weight of said inorganic perchlorate salt per 100 parts by weight of aluminum hydroxide.
 19. An insulated electrical conductor comprising a metallic conductor, a first insulating layer comprising flexible polyvinyl chloride surrounding said conductor, and a second layer surrounding said first insulating layer, said second layer comprising the composition of claim 6
 20. The insulated electrical conductor of claim 19, wherein said second layer comprises a second flame retardant.
 21. The insulated electrical conductor of claim 20, wherein said second flame retardant is antimony trioxide.
 22. In an aluminum hydroxide containing plastic composition whose major polymeric constituent is polyvinyl chloride, the improvement consisting of inclusion therein of an amount, effective in diminishing discoloration of said composition upon heating at 177° C., of at least one inorganic perchlorate salt selected from the group consisting of alkali metal perchlorates and alkaline earth metal perchlorates. 